The idea of a "tautology" and especially of its use in philosophical debate, has bugged me for years. Let me express my analytical (or synthetic) reaction here and see if I get an illuminating response. Many of those who dislike the idea of evolution, or Darwinian evolution anyway, make a point about the nature of the alleged mechanism. The notion that evolution works by "the survival of the fittest" can not, they say, be a substantive insight at all because it is a tautology. The fittest are defined by survival, and then survival is attributed to their fitness. An obvious circle. Likewise, those who dislike the notion of market efficiency make the same point, though they may not recognize its similarity. They say that the notion of efficiency is defined by what the market does, and then the market is said to be efficient. An obvious and invalidating circle! Another example: those who argue that a God is necessary, and must be postulated even if His existence ca...